1. Field of the Invention
The present invention relates to a printed board for mounting electronic components, such as LSIs, capacitors and resistors, thereon, in particular to a printed board including a wiring pattern for detecting deterioration of a printed board early, and to a manufacturing method of the printed board.
2. Description of the Related Art
Industrial machines, such as machine tools, are required to maintain reliability for a long period of time. However, deterioration of a printed board inside a machine due to environmental stress is inevitable. For example, under a plant environment where industrial machines are used, mist caused by cutting liquid which is generated with a processing of a workpiece enters a housing of electric and electronic devices, such as a controller, and is attached on a surface of a printed board on which electronic components are mounted. There is a problem that the mist deteriorates a wiring pattern formed on the printed board due to corrosion or electric corrosion to cause a failure of electric and electronic devices.
As a method for detecting such deterioration of the printed board, there is a known art that a wiring pattern for detecting deterioration having a structure that deteriorates earlier than a regular wiring pattern is previously provided for the printed board, and advance detection of deterioration is made possible before a regular function of the printed board is impaired by monitoring electronic properties of the wiring pattern for detecting deterioration.
FIG. 10 is a view showing a cross-sectional structure of a printed board on which a conventional wiring pattern for detecting deterioration is formed. In a printed board 1, a wiring pattern 3 for detecting deterioration is formed on a surface of an insulating substrate 4.
The surface of the insulating substrate 4 on which the wiring pattern 3 for detecting deterioration is formed is covered by solder resist 2 together with the wiring pattern 3 for detecting deterioration.
As a structure of the wiring pattern for detecting deterioration in prior art, Japanese Unexamined Patent Application Publication No. 2001-251026 discloses a wiring with a narrower width than other wirings and a wiring with a narrower insulating gap. Further, Japanese Unexamined Patent Application Publication No. 2001-358429 discloses a structure in which solder resist on the wiring pattern for detecting deterioration is formed into a thin film. Further, Japanese Unexamined Patent Application Publication No. 10-62476 discloses a structure in which solder resist is not formed on the wiring pattern for detecting deterioration in the first place.
Deterioration of a printed board due to mist of cutting liquid or the like is significant particularly in areas where mist is easily accumulated. Therefore, the wiring pattern for detecting deterioration is not necessarily deteriorated first even in the cases where solder resist on the wiring pattern for detecting deterioration is formed thin, solder resist is not formed, or a width or an insulating gap of the wiring pattern is made narrower as in the prior art, and there is a problem that guideline of preventive maintenance for the printed board is difficult to be obtained. Further, there is a problem that yield in a printed board manufacturing process is reduced when the pattern width or the insulating gap is made extremely narrower than the regular wiring pattern.